Method and system for motor failure detection

ABSTRACT

Systems and methods for detecting developing faults in a flow generator or ventilator during therapeutic use thereof are provided. The motor current may be measured to estimate the torque input by the motor, while the output torque from the impeller may be determined (e.g., as inferred from the motor control system model and/or by consulting a lookup table). One or more transducers may collect data useful in determining the input and output torques. A difference between the input (to the motor) torque and the output (from the impeller) torque may be calculated. The difference, optionally filtered using a low-pass filter to reduce noise, may be compared to a predetermined threshold once or over a period of time to detect gross failures and/or developing failures. Once a failure or developing failure is detected, a user may be alerted and/or the flow generator may be placed into a “service required” mode.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/081,232, filed Apr. 11, 2008, which claims the benefit of ApplicationSer. No. 60/907,717 filed on Apr. 13, 2007, the entire contents of whichis hereby incorporated herein by reference.

FIELD OF THE INVENTION

The example embodiments disclosed herein relate to systems and/ormethods for motor failure detection in mechanical devices, e.g., devicessuitable for treating respiratory insufficiency/failure and/orsleep-disordered breathing (SDB), such devices implementing, forexample, non-invasive techniques (using, for example, mask systems, flowgenerators or ventilators, positive airway pressure (PAP) devices, etc.)and/or invasive ventilation, volume modes, mechanical ventilation,and/or other like techniques. More particularly, the example embodimentsdisclosed herein relate to systems and/or methods that detect developingmotor failures by comparing the input torque and output torque of a flowgenerator/ventilator.

BACKGROUND OF THE INVENTION

Obstructive Sleep Apnea (OSA) and other dangerous sleep-disorderedbreathing (SDB) conditions affect thousands worldwide. Numeroustechniques have emerged for the treating SDB, including, for example,the use of Continuous Positive Airway Pressure (CPAP) devices, whichcontinuously provide pressurized air or other breathable gas to theentrance of a patient's airways via a patient interface (e.g. a mask) ata pressure elevated above atmospheric pressure, typically in the range3-20 cm H₂O. Typically, patients suspected of suffering from SDBregister with a certified sleep laboratory where sleep technicians itpatients with numerous data collectors and monitor their sleep activityover a given period. After the patient is diagnosed, a treatment regimenusually is developed, identifying both a treatment apparatus (ortreatment apparatuses) and program of use for the treatmentapparatus(es).

FIG. 1 shows a simplified schematic of a typical CPAP treatmentapparatus. An impeller 1 is powered by an electric motor 2 using a servo3 under the direction of a microprocessor-based controller 4. The supplyof breathable gas is carried to the mask 5 through a flexible conduit 6.The apparatus has various switches 7, displays 8, and a number oftransducers. The transducers may monitor a number of processes, such as,for example volumetric flow rate 10 (e.g., at a predetermined point inthe flow path), pressure 11 (e.g., at a predetermined point downstreamof the flow generator outlet or at the mask), snore 12, flow generatorrotational speed 13, and/or motor parameters 14.

It would be advantageous to detect faults in the treatment apparatus asthey develop during the operation of the blower. A gross failure of amotor bearing and/or turbine results in the patient ceasing to receivetreatment. However, if a motor bearing and/or turbine begin(s) to fail,a patient may receive sub-optimal treatment for the period of timebetween the beginning of the failure and when the failure is complete. Afailing motor may result in low (or lower than expected) pneumaticoutput. Failing to recognize developing faults also may cause thebearing to overheat, which may, in turn, result in a potential hazards.

To this end, U.S. Pat. No. 5,621,159, the entire contents of which isincorporated herein by reference, discloses techniques for determiningincreased rotational friction. Unfortunately, further improvements tothese techniques are necessary, as they require powering down the fanfor a predetermined period to check the spin-down rate, which makes suchtechniques inappropriate for flow generators actually in use.

Certain other techniques for detecting faults are described in AU764761, and U.S. Pat. Nos. 6,591,834, 6,745,768, and 7,040,317, theentire contents of each of which is hereby incorporated herein byreference. Further improvements to these techniques also would beadvantageous, as there are certain faults that cannot be detected usingsuch techniques. For example, such techniques generally cannot determinewhether there is a faulty bearing that is not yet causing a “motorstalled” condition or a near-motor-stalled condition. It would beadvantageous to detect other failures, such as, for example, low outputtorque, increased bearing friction, constricted inlet(s), faulty ordisconnected Hall sensor(s), etc.

Thus, it will be appreciated that there is a need in the art forimproved motor fault detection techniques.

SUMMARY OF THE INVENTION

One aspect of certain example embodiments relates to a holistic approachto detecting faults in a flow generator. Such faults may include, forexample, degraded bearings, a failing motor, low output torque,increased bearing friction, constricted inlet(s), dropped phase,disconnected Hall sensor(s), rubbing/loose/fragmented impeller, etc.

Another aspect of certain example embodiments relates to comparing theexpected and monitored load torque of a flow generator, with theexpected load torque being known beforehand and specific to a particularflow generator (or model of flow generators), and the monitored loadbeing calculated and/or inferred from a model and/or lookup table.

Still another aspect of certain example embodiments relates totechniques for detecting faults in a flow generator without suspendingoperation of the flow generator.

Yet another aspect of certain example embodiments relates to techniquesfor detecting developing faults in a flow generator.

The techniques of certain example embodiments can be applied to anydevice having a motor (e.g., with a bearing) to detect faults thereinby, for example, comparing the useful (output) torque produced by thesystem with the (input) torque generated by the motor. These techniquesmay be used for motor testing and/or fault detection (e.g., gross faultdetection, developing fault detection, and the like) before the motor isincorporated into the device, as a diagnostic function of an assembleddevice, etc.

In certain example embodiments, a method is provided to detectdeveloping faults in a flow generator during therapy. A flow generatormay employ an impeller powered by a motor under servo control. Thetorque exerted on the impeller by the fluid load is estimated frommeasured parameters. This is the output (e.g., useful) torque. The motortorque (e.g., input motor torque) can be determined in part from motorcurrent. A difference between the input torque and the output torque maybe calculated. The determination of whether a fault exists may be basedat least in part on an assessment of the difference. The term expectedmotor torque alternatively may be used to signify the torque that isexerted on the impeller expected from the measured outputs from theturbine, including, for example, measured pressure, flow, and/orrotational speed.

In certain other example embodiments, a turbine-based ventilator deviceis provided. An impeller may be powered by a motor under servo-control.The system's servo-controller may be further configured to indicate thepresence of developing faults of the turbine-based ventilator deviceduring therapeutic use of the turbine-based ventilator device based on acomparison of useful output torque (e.g., based on measured parameters)and the input (e.g., motor) torque. The turbine-based ventilator devicemay be a flow-target, volume-target, or pressure-target device, incertain example embodiments. Also, the turbine-based ventilator devicemay be a PAP device in certain example embodiments.

Optionally, the difference may be filtered to reduce noise. Thedifference, filtered or unfiltered, may be used to assess whether afault exists, based on, for example, a comparison (or comparisons) withat least one predetermined threshold. It will be appreciated thatcertain example embodiments described herein may be in connection withthe treatment of SDB (e.g., OSA) via non-invasive (e.g., mask)ventilation and/or positive airway pressure devices. However, certainexample embodiments may be used in connection with invasive ventilationtechniques, volume modes, and/or beyond SDB to mechanical ventilation ingeneral. By way of example and without limitation, such techniques maybe applicable whenever the safe operation with oxygen is a concern,which often is the case in general ventilation.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings facilitate an understanding of the variousembodiments of this invention. In such drawings:

FIG. 1 shows a simplified schematic of a typical CPAP treatmentapparatus;

FIG. 2 shows the relationship between drive and the r.m.s. supplycurrent for six different constant angular velocities experimentallyobtained from an AutoSet CS2 blower, which is commercially availablefrom ResMed;

FIG. 3 shows the results of modeling the r.m.s. current as a nonlinearfunction of drive and angular velocity;

FIG. 4 shows two plots of torque in Newton-meters vs. time;

FIG. 5 shows a close-up of one cycle in FIG. 4;

FIG. 6 shows the same scenario, this time with a perturbation of theload torque between 15 and 25 seconds;

FIG. 7 shows the expected torque difference;

FIG. 8 shows longer-term monitoring of the torque-balance trace in FIG.7 for four separate units; and,

FIG. 9 is an illustrative flowchart showing a fault detection method, inaccordance with an example embodiment.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

1. Fault Detection

Certain example embodiments relate to techniques for detectingdeveloping faults in flow generators. This may be made possible bycalculating the difference between the expected and monitored loadtorques of a flow generator. The difference, filtered or unfiltered, maybe compared to one or more predetermined thresholds (e.g., over a periodof time) to determine whether a gross fault has occurred and/or whethera fault is developing. The following sections detail illustrativeequations and illustrative hardware/software configurations that may beused in conjunction with this approach.

1.1 Model Overview

The blower is powered by a motor 2 that delivers a torque to theimpeller 1 which accelerates the delivered fluid. At any point in time,there will be a balance between the torque developed by the motor andthe torque required for accelerating the fluid, accelerating the mass ofthe impeller and motor rotor, and any losses in the system. It will beappreciated that this balance also could be formulated in terms ofpower. The torque developed by the motor can be calculated from thecurrent consumed by the motor by applying the motor constant k_(m). Fora multiphase motor, this constant will be a per-phase equivalentconstant. The torque provided by the motor is then:T _(m) =k _(m) ·I _(m),  (1)where I_(m) is the motor current. This torque is balanced by the torquesdetailed above as in the equation:

$\begin{matrix}{{T_{m} = {\frac{p \cdot Q}{\omega} + {J\frac{\partial\omega}{\partial t}} + T_{loss}}},} & (2)\end{matrix}$where p is the pressure delivered to the patient in Pascals (or thedifference in pressure between the outlet and inlet of the impeller ifthe inlet pressure is not zero), Q is the flow-rate in m³·s⁻¹ of thedelivered gas, co is the rotational speed of the impeller in radians persecond (which may be measured directly or indirectly, e.g., as somebrushless DC or “sensorless motors” are capable of inferring rotationalspeed from back-emf), J is the rotational moment of inertia of all thespinning mass that the motor is accelerating, and T_(loss) is the sum ofall the loss torques. The last term in equation (2) can be modeled, forexample, using the following function:T _(loss) =T _(cons)+ƒ(p,Q ²,ω).  (3)

It will be appreciated that here, the density, viscosity, andtemperature of the fluid are assumed to be constant. When this is nottrue, certain example embodiments may allow constants to be incorporatedto allow for measured and/or inferred changes in these and/or othervariables. The rationale for this last equation is as follows. T_(cons)represents a “constant torque load” typical of rotating machinery. Atorque proportional to ω is a viscous torque attributable tofluid-filled ball bearings. A torque term proportional to the pressureacross the impeller will account for leakage from high pressure zones tolow pressure zones, and a torque proportional to Q² will allow for the(mostly turbulent) losses along the fluid path of the impeller andhousing. In certain example embodiments, the function ƒ may be assumedto be approximately linear, although the present invention is not solimited. For example, in certain other example embodiments, the functionƒ may be nonlinear, a lookup table, etc. One example of a suitablefunction is:T _(loss) =T _(cons) +k ₁ ·ω+k ₂ ·Q ² +k ₃ ·p  (4)

For the purposes of the discussion herein, SI units will be used,implying that torque will be measured in Newton-meters. Of course, itwill be appreciated that other units of measurement can be used in otherexample embodiments.

Certain example embodiments relate to a therapy device having a motorand an impeller as above, transducers suitable for measuring and/orcalculating p, Q, ω, I_(m). Such capabilities allow the torque balancein equation (2) to be monitored. For example, when the differencebetween the left-hand-side term and the sum of the right-hand-side termsexceeds a predetermined threshold, a signal may be generated to indicatethat service is necessary (e.g., an audible alarm and/or visual alarmmay be triggered, the flow generator may be placed into a “requiresservice” mode, etc.). As another example, the balance can be trackedover time to give an indication of expected remaining service life or“health status.” It will be appreciated that the term related torotational inertia

$\left( {J\frac{\partial\omega}{\partial t}} \right)$could be ignored if the torque balance were only checked duringnon-acceleration periods.

Thus, in certain example embodiments, the predetermined threshold may beindicative of a value signifying a gross failure, whereas thepredetermined threshold may be indicative of a relative (e.g., growing)failure in certain other example embodiments. Certain exampleembodiments may be capable of indicating both gross failures (e.g., asingle difference being above a given threshold), as well as relativefailures (e.g., increasing differences between the monitored andexpected torques beyond a threshold indicative of an acceptableincrease). The predetermined threshold may be expressed in terms of anabsolute value, a percentage increase or decrease, etc.

1.2 Calculation of T_(m)

Equation (1) shows that the torque provided by the motor can becalculated as the product of the motor current and the motor torqueconstant. Ordinarily, the motor torque constant will be provided by themotor manufacturer. The motor supply current then only needs to bemeasured or inferred to complete input to this equation. Accordingly, ifa low-valued resistor is placed in line between the power supply and themotor, then the voltage across that resistor will be approximatelylinearly proportional to the current supplied to the motor. Also, if themotor is controlled using switched-mode technology, then the voltageacross the resistor may need to be filtered to provide a substantiallynoise-free estimate of supply current.

The motor supply current also can be inferred from other parametersinvolved in the closed-loop control of motor current. For example, atransconductance amplifier can be used to control motor current in aclosed loop fashion. Here, a control voltage, known as “drive,” is theinput to the transconductance amplifier that uses switch-mode technologyto control the current fed to the motor. At a substantially constantangular velocity of the motor, there will be an almost-linearrelationship between the control voltage “drive” and the motor supplycurrent. FIG. 2 shows the relationship between drive and the r.m.s.supply current for six different constant angular velocitiesexperimentally obtained from a AutoSet CS2 blower, which is commerciallyavailable from ResMed. The plots correspond, from left to right, to RPMsof 5,000; 8,000; 10,000; 15,000; 20,000; and 23,000.

The change in the relationship between drive and supply current withangular velocity can be accommodated by a model or lookup table thatcovers the required operating range. Because the transconductanceamplifier loop may run at a very high speed (e.g., about 20 kHz), themodel or lookup table can be created using static tests (e.g., tests ata substantially constant velocity), but the results will still be validgenerally for a dynamically changing system (e.g., where the motor isaccelerating). FIG. 3 shows the results of modeling the r.m.s. currentas a nonlinear function of drive and angular velocity. The plotrepresents the same data as those plotted in FIG. 2 and displays asubstantially linear relationship between modeled and real r.m.s.current. The slope of the line is approximately one, the y-intercept isabout zero, and the correlation coefficient is about 0.998. It will beappreciated that this model could also be implemented by a lookup table.

1.3 Calculation of the Torque Required to Accelerate the Breathable Gas

The power produced by a pump is equal top p·Q, where, if p is measuredin Pascals and Q in m³·s⁻¹, the result will have units of Watts. If thepower produced by the pump is divided by the angular velocity in radiansper second, the result is torque in Newton-meters. If the pump is 100%efficient (e.g., no fluid or mechanical losses), then this torque isthat required of the motor when the pump is turning at constant angularvelocity.

1.4 Calculation of the Torque Required to Accelerate the Spinning Massof the Pump and Motor Rotor and Shaft

If the motor and pump are accelerating (e.g., the angular velocity isnot constant), then a torque will be required to accelerate the combinedspinning mass as:

$\begin{matrix}{{T_{inertia} = {J\frac{\partial\omega}{\partial t}}},} & (5)\end{matrix}$where J has the SI units of kg·m², T_(inertia) has units ofNewton-meters, and

$\frac{\partial\omega}{\partial t}$has units of (radian)·s⁻².

For the AutoSet CS2 blower, the value of J is 2·1.13 E⁻⁶ (twoimpellers)+1.26 E⁻⁷ (motor)=2.386 E⁻⁶ kg·m².

1.5 Calculation of the Torque Consumed by the Bearings and PumpInefficiencies

As noted above, the inefficiencies of the pump and losses related to thebearings can be modeled empirically while still basing the functionalprinciples of certain example embodiments on sound physical principles.One such model isT _(loss) =T _(cons) +k ₁ ·ω+k ₂ ·Q ² +k ₃ ·p.  (6)

Here, T_(cons) represents the static or Coulomb friction of thebearings, and k₁ represents the viscous friction typical ofgrease-filled bearings. k₂ represents the (predominantly turbulent)fluid losses within the pump housing, and k₃ represents losses relatedto leakage from high pressure zones to low pressure zones.

Typical values of the constants above for a AutoSet CS2 blower areT _(cons)=5.472.1E ⁻⁴N·m.k ₁=1 0.8838E ⁻⁶N·m·(radian⁻¹)·sk ₂=1.2585E ²N·m⁻⁵·(radian⁻¹)·s²k ₃=1.0493E ⁻⁷N·m·Pa⁻¹These values were calculated using a “known-good” unit and a leastsquares fitting routine. It will be appreciated that constants for otherunits may be calculated using the same or similar techniques.

1.6 an Example of Dynamically Calculated Torque Difference

FIG. 4 shows two plots of torque in Newton-meters vs. time, the dottedcurve being that supplied by the motor and the solid curve being thatrelated to the combined load. The AutoSet CS2 blower is here deliveringpressure in simple bilevel fashion with a fixed cycle length while asubject breathes. The motor torque was calculated using the modeldeveloped with static tests, e.g.,T _(m)=ƒ(drive,ω)  (7)It will be appreciated that motor current also can be calculated as afunction of drive (representing the [0, 1] signal output by the motorcontroller) and speed of the motor spindle, as modeled by the equationT_(m)=ƒ(drive, RPM).

FIG. 5 shows a close-up of one cycle in FIG. 4, showing goodcorrespondence (e.g., torque balance) between the two signals. FIG. 6shows the same scenario, this time with a perturbation of the loadtorque between 15 and 25 seconds. The perturbation included a smallamount of friction being applied to the impeller surface. As will beappreciated from FIG. 6, the motor torque curve is shifted up during theperturbation, e.g., the motor is supplying some “extra” torque notmatching the expected load. FIG. 7 shows the expected torque difference,and again there is a pronounced difference in the balance during theperturbation.

2. An Example of Longer-Term Monitoring of Blower “Health” Status

FIG. 8 shows longer-term monitoring of the torque-balance trace in FIG.7 for four separate units. In FIG. 8, the displayed traces have beenfiltered with a time constant of 100 seconds to eliminate transientnoise. Three “good” units (curves 810, 820, and 830) were run for aroundone hour and displayed similar near-zero torque difference. A fourthcrippled unit (curve 840) was run for about three hours until bearingfailure. This unit had had the grease removed from its bearing at timezero and at the one hour point some dust was introduced into thebearing. The crippled unit clearly displays a greatly increased torquedifference, indicating that the motor is supplying torque (or power) toan “unexpected” load. It will be appreciated that this unit could havebeen shut down by the controlling software long before catastrophicfailure based at least in part on the detection of the large filteredtorque difference.

3. Illustrative Flowchart Showing Fault Detection Example Methods

FIG. 9 is an illustrative flowchart showing a fault detection method, inaccordance with an example embodiment. In step S902, the motor currentis measured, and the motor torque is determined. The motor torque can becalculated, for example, using equation (2). Alternatively, the motortorque can be inferred using a model and/or lookup table of the motorcontrol system, for example, using equation (7). In step S904, thetorque balance (e.g., the balance between what the motor is supplyingand the expected load) of the blower is monitored, for example, usingequation (2). The difference between the expected and monitored (actual)load may be calculated in step S906. The difference may be modeled as:Δ=T _(m) −T _(load),  (8)with T_(load) being the right-hand side of equation (2).

In step S908, A may be filtered with an appropriate low-pass filter toreduce unimportant transient errors, producing Δ. In step S910, Δ may bereported as part of a maintenance interrogation (e.g., by the controller4 and output via one or more displays 8), reflecting the “health” of theflow generator. As shown in step S912, if Δ is greater than apredetermined threshold for a specified amount of time, the flowgenerator may be shutdown, put into a “service mode,” and/or mayotherwise alert a user that a fault is detected and/or anticipated. Itwill be appreciated that the predetermined threshold and/or the amountof time may be particular to the model of the flow generator being used.

The monitoring and/or calculating processes may be performed and/oraggregated over a longer period of time. This data may be stored (e.g.,to a memory) and compared for longer-term trending purposes to measurethe overall health of the flow generator and/or changes to the overallhealth of the flow generator. For example, the actual performance may becompared to an idealized performance over a longer period of time.Significant deviations from the idealized performance may be indicativeof a problem with the flow generator and/or the monitoring equipment.

It will be appreciated that although certain example embodiments havebeen described in relation to a CPAP device and/or to ResMed's AutoSetCS2 model blower, the present invention is not so limited. Instead, theexample embodiments described herein may be used in conjunction withother types of flow generators (e.g., PAP devices generally, bileveldevices, AutoSet algorithm devices, etc.), potentially available fromany manufacturer. Also, it will be appreciated that the hardwarecomponents described herein are not limited to any particulararrangement. For example, the transducers may be a part of a particularflow generator, they may be part of a separate module to be integratedinto a particular flow generator, they may be separate from a particularflow generator, etc. Moreover, it will be appreciated that the hardwareand/or software components described herein may comprise any combinationof hardware, software, firmware, or the like that provides suitablefunctionality. For example, the calculations may be implemented bysoftware algorithms executable and/or embedded into the controller 4.

One advantage of certain example embodiments relates to patientsbenefiting from increased safety and the knowledge of impendingfailure(s). Another advantage of certain example embodiments relates todeveloping fault detection without the need for temperature and/or othersensors, as enabled by, for example, software algorithms transformingdata already monitored by hardware elements of the treatment apparatus.The detectable faults may include, for example, degraded bearings, afailing motor, low output torque, increased bearing friction,constricted inlet(s), dropped phase, disconnected Hall sensor(s),impeller failures, etc.

It will be appreciated that although certain example embodiments havebeen described as relating to PAP devices and/or flow generators, thepresent invention is not limited to any particular device. For example,the example embodiments described herein may be used in connection withany suitable turbine-based ventilator. Such turbine-based ventilatorsmay include, for example, flow, volume, and/or pressure target baseddevices. Such turbine-based ventilators also may include, for example,traditional mechanical ventilators, CPAP devices, high-flow nasalcannula based devices, etc.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the invention. Also, the various embodiments described abovemay be implemented in conjunction with other embodiments, e.g., aspectsof one embodiment may be combined with aspects of another embodiment torealize yet other embodiments.

Also, the various embodiments described above may be implemented inconjunction with other embodiments, e.g., aspects of one embodiment maybe combined to provide treatment in connection with invasive ventilationtechniques, volume modes, mechanical ventilation, etc. In addition,while the invention has particular application to patients who sufferfrom OSA, it is to be appreciated that patients who suffer from otherillnesses (e.g., ventilatory insufficiency or failure, congestive heartfailure, diabetes, morbid obesity, stroke, barriatric surgery, etc.) canderive benefit from the above teachings. Moreover, the above teachingshave applicability with patients and non-patients alike in non-medicalapplications.

What is claimed is:
 1. A method of detecting developing faults in a flowgenerator having an impeller powered by a motor under servo-controlduring operation of the flow generator, the method comprising: supplyinga flow of pressurized breathable gas generated by the flow generator;measuring, with a first transducer, at least one input parametersupplied to the motor when the flow generator is generating the flow ofpressurized breathable gas; determining, with a controller having aprocessor, an input motor power value provided to the motor, the inputmotor power value based at least in part on the at least one inputparameter measured by the first transducer; measuring, with a secondtransducer, at least one output from a turbine of the motor;determining, with the controller, a load motor power value, the loadmotor power value based at least in part on the at least one measuredoutput measured by the second transducer; calculating, with thecontroller, a difference between the load motor power value and theinput motor power value, the difference being associated with losses inthe motor; and assessing, with the controller, whether a fault isdeveloping in the flow generator based at least in part on thedifference by comparing the difference to a predetermined threshold. 2.The method of claim 1, wherein the determination of the input motorpower value with the controller is further based on an inference from amotor control system model.
 3. The method of claim 1, wherein thedetermination of the input motor power value with the controller isfurther based on a motor control system lookup table.
 4. The method ofclaim 1, further comprising activating an alert and/or placing the flowgenerator into a service required mode when development of a fault hasbeen assessed by the controller.
 5. The method of claim 1, furthercomprising indicating development of a fault with an audible alarmand/or a visual alarm when the difference calculated by the controllerexceeds the predetermined threshold for a specified amount of time. 6.The method of claim 1, further comprising filtering the difference witha low-pass filter.
 7. The method of claim 6, wherein the low-pass filteris configured to reduce transient errors.
 8. The method of claim 6,further comprising comparing the filtered difference to thepredetermined threshold.
 9. The method of claim 8, further comprisingindicating development of a fault with an audible alarm and/or a visualalarm when the filtered difference calculated by the controller exceedsthe predetermined threshold for a specified amount of time.
 10. Themethod of claim 1, further comprising correcting for variations in oneor more of ambient pressure, temperature, and viscosity with thecontroller.
 11. The method of claim 1, wherein the at least one measuredoutput includes pressure, flow, and/or rotational speed.
 12. The methodof claim 1, wherein the motor is a DC motor.
 13. The method of claim 1,wherein the at least one input parameter is voltage supplied to themotor.
 14. The method of claim 1, wherein the at least one inputparameter is motor current supplied to the motor.
 15. A turbine-basedventilator device to supply a flow of pressurized breathable gas,comprising: a motor configured to drive an impeller to generate the flowof pressurized breathable gas to be supplied; a first transducerconfigured to measure at least one input parameter supplied to the motorwhile the motor is generating the flow of pressurized breathable gas; atleast one additional transducer configured to measure at least oneoutput from a turbine of the motor; and, a closed-loop controllerconfigured to control the motor, wherein the controller is furtherconfigured to detect a developing fault of the device during operationof the device, the developing fault being detected based on a comparisonof an input motor power value and a load motor power value, and whereinthe input motor power value is based at least in part on the at leastone input parameter measured by the first transducer, and wherein theload motor power value is based at least in part on the at least onemeasured output measured by the at least one additional transducer. 16.The device of claim 15, further comprising a flexible conduit connectedto a patient interface, the conduit and the patient interface beingsuitable for conveying a supply of pressurized breathable gas to thepatient.
 17. The device of claim 15, wherein the at least one inputparameter is voltage supplied to the motor.
 18. The device of claim 15,wherein the at least one input parameter is motor current supplied tothe motor.
 19. The device of claim 18, wherein the first transducercomprises a transconductance amplifier configured to measure motorcurrent.
 20. The device of claim 15, wherein the at least one outputincludes at least one of: pressure delivered to a patient, flow,rotational speed of the impeller, and motor current.
 21. The device ofclaim 15, wherein the input motor power value is further based, at leastin part, an inference from a motor control system model.
 22. The deviceof claim 15, wherein the input motor power value is further based, atleast in part, a motor control system lookup table.
 23. The device ofclaim 15, wherein the controller is further configured to activate analert and/or place the device into a service required mode when thedeveloping fault is detected.
 24. The device of claim 15, wherein thecontroller is configured to instruct the motor to correct for variationsin ambient pressure and/or temperature.
 25. The device of claim 15,wherein turbine-based ventilator is a flow-target, volume-target, and/orpressure-target device.
 26. The device of claim 15, wherein theturbine-based ventilator device is a PAP device.
 27. The device of claim15, further comprising a low-pass filter configured to filter thecomparison.
 28. The device of claim 27, wherein the low-pass filter isconfigured to reduce transient errors.
 29. The device of claim 27,wherein the controller is further configured to compare the filteredcomparison to a predetermined threshold.
 30. The device of claim 29,wherein the controller is further configured to indicate the developingfault when the filtered comparison exceeds the predetermined thresholdfor a specified amount of time.
 31. The device of claim 15, wherein thecomparison is a difference between the load motor power value and theinput motor power value, the difference being associated with losses inthe motor.
 32. The device of claim 31, wherein the controller is furtherconfigured to compare the difference to a predetermined threshold. 33.The device of claim 32, wherein the controller is further configured toindicate the developing fault when the difference exceeds thepredetermined threshold for a specified amount of time.
 34. The deviceof claim 15, wherein the motor is a DC motor.